Thermionic cathode



Oct. 15, 1940. GQOSKENS 2,218,381

THERMIONIC CATHODE Filed Aug. 1'7. 195? Inventor: Henricus Cvooskeris,

Attorney I Patented Oct. 15, 1940' UNITED STATES PATENT. OFFICETHERMIONIC CATHODE Henricus Gooskens, Eindhoven, Netherlands, assignorto General Electric Company, a corporation of New York Applica ionAugust 17, 1937, Serial No. 159,595

Germany September 3, 1936' Claims. (01. 176-126) The present inventionrelates to improvements The utility of the invention may best be exither i ni cathodes. plained in connection with the single figure of theIt is an object of the invention to provide an attached drawing, whichrepresents a mercuryemitting substance which is strongly resistant tovapor discharge device I surrounded by an en- 5 high temperatures in thesense of having a low closing envelope 2, the device being of the type 5rate of evaporation when exposed'to such temin which a mercury pressurein excess of 5 atmosperatures, pheres occurs during normal operation. Atsuch This object is attained by utilizing as an emitpressures, thedischarge may be concentrated on ter a. glass-like substance comprisinga multiple relatively small portions of the discharge elecoxide having avery high boiling point, say above trodes which are represented at 3 sothat there is 10 2,000 degs. C. According to a preferred embodia strongtendency for the electrode material to meat of the invention, I maycombine for this be vaporized. This diificulty may be overcome purpose abasic component comprising one or by forming the electrodes of overwoundtungsten more oxides of the group consisting of thorium, or a. similarrefractory base material to which is zirconium, beryllium and lanthanumwith an acid applied a layer of emitting material of the type 15component comprising one or more oxides of the hereinbefore described.One example of such group consisting of silicon and aluminum. Inemitting material may be prepared and applied the selected combinationthe basic component as indicated in the following:

should be present in excess so that in the case of 100 grams thoriumoxide, 35 grams of a mix- 0 the thorium-silicon combination, forexample, the ture of barium carbonate and strontium carformula of theemitting substance may be reprebonate, 165 cc. of a 3% solution ofcellulose in sented as'XThOa-SiOz, where X represents a amyl acetate,and 165 cc. amyl acetate are mixed number greater than 1. (When speakingof an together and finely ground. To this mixture 22 acid or basiccomponent I imply that the comgrams of finely ground quartz (SiOz) areadded 5 ponent is acid or basic with respect to the other and themixture is again ground. From the 25 component.) Paste which is obtainedin this manner, an even It is not only desirable to have the boilingthin layer is applied to the tungsten core and P n f the emittingsubstance as a whole above the electrodes are heated in a reducingatmos- 2,000 degs. C. but it is also advisable that the phere, forinstance in a nitrogen-hydrogen mixbasic component have a still higherboiling point, ture. The elements may be maintained at a very 30 sayabove 3,000 degs. C. in order that selective high temperautre, (forinstance 2,000 degs. C.) evaporation of the surplus of this componentuntil sintering takes place and a fused glass-like may be prevented. Allof the basic components mass is obtained on the electrode. The substanceenumerated inthe preced g pa p fulfill resulting from the heating stepmay be conthis requirement. When using several bas c comvenientlyreferred to as the fusion product of 35 ponents, as is advantageous insome case Only the oxides employed. After this, the electrode veryslight evaporation occurs when only one of may be introduced in thedischarge tube and the the basic substances has a boiling point abovelatter may be then completed. With such elec- 3,000 degs. C. trodes, a,life of several thousand hours may be 4 Em tti sub e constituted asdescribed in attained without'the emitting material evaporat- 40 theforegoing assume a glass-like quality when ing considerably, subjectedto h gh te pe t res, a silicate being While I have described particularembodiments formed when silica is used as the ac d mp n of theinvention, numerous modifications thereof a d an aluminate when aluminumoxide is may be made by those skilled in the art without p y Tests haveshown that electrodes (111? departing from the invention. I thereforeaim 45 structed in accordance the invention are in the appended claimsto cover all such equivhighly resistant to high temperatures and v alentvariations as fall within the true spirit and orate only very slightly,so that a long electrode scope of t foregoing disclosure, life isobtained. Their electron emissivity may w t I claim as new and desire tsecure by ,50 advantageously be increased in some instances LettersPatent of the United States is:

by the addition of an alkaline earth material, for 1, th r i i cathodecomprising a coating ex p barium Strontium Oxide- These of a glass-likeemitting substance which includes ter combine with the acid component ofthe ,the fusion product of a basic component comemitting substance andform therewith a silicate prising one or more oxides of the groupconsistor aluminateasthe case may be. ing of thorium, zirconium,beryllium and lan- 55 thanum with an acid component comprising one ormore oxides of the group consisting of silicon and aluminum 2. Athermionic cathode comprising an exposed discharge-receiving surfacecoated with a glasslike emitting substance constituted of the fusionproduct of a basic component comprising one or more oxides of the groupconsisting of th zirconium, beryllium or lanthanum with an acid.

component comprising one or more oxides of the group consisting ofsilicon and aluminum, the basic component being present in excess.

3. A cathode according to claim 2 characterized by the fact that theemitting substance also includes alkaline earth material.

4. A thermionic cathode comprising an exposed discharge-receivingsurface coated with a glasslike emitting substance, said substanceincluding the fusion product of a multiple oxide of thorium and silicon,the thorium component being present in excess.

5. A thermionic cathode having an exposed discharge-receiving surfacewhich is coated with a temperature-resistant emitting substance, saidsubstance includingthe fusion product of the oxides of thorium andsilicon and further including a quantity of alkaline earth material.

HENRICUS GOOSKENS.

